1. Field of the Invention
This invention relates to coating and/or reinforcing various substrates with polymeric fibers formed from fiber forming polymer solutions. More particularly, this invention relates to an apparatus in which the polymeric fiber reinforcement and/or coating is applied to the substrate by oscillating the substrate as it is continously passed through a solution of fiber forming polymer.
2. Description of Related Art
Fabrics can be produced from polymers by weaving, knitting or non-woven techniques. All fabric-forming techniques require polymerization, polymer recovery and formation of filaments. In woven and knitted fabrics, the polymer is processed into a filament and then into a multi-filament yarn before being woven or knitted into a fabric by interlacement of warp and weft threads. Non-woven fabrics are manufactured from a web, sheet or batt of chopped fibers that are joined by mechanical, chemical or solvent processes. Barbed needles have been used to punch into a web of fibers to entangle them. The fibers can be bonded into a felt by applying heat, moisture and pressure to a sheet of fibers. The term non-woven is also applied to fabrics comprising a web of fibers held together by sticking. The non-woven fabrics are very soft but have very little overall strength. All of these fabric forming techniques are capital and labor intensive, requiring complex multistage processing to convert raw polymer stock into knitted or woven fabric or a non-woven fibrous sheet.
A one-step process for forming shaped, fibrous polymer networks is disclosed in U.S. Pat. Nos. 4,127,624; 4,198,461; 4,397,907; and 4,403,069. The process involves an in situ fiberization (ISF) technique based on agitation-induced crystallization of the fibers from solution. The fibers form a coherent, three-dimensional, isotropic network of crystalline fiber bundles. The three-dimensional mass of fibers is produced by cooling a container of the solution which is being agitated at sonic frequency. This ISF technicue can be used to form a fiber mass which may subsequently be impregnated with a curable polymeric resin to provide a fiber reinforced composite which is useful as a structural material or as a high strength encapsulant for electronic components. In addition, the fiber mass so formed may be broken into individual fibers or fiber bundles which are useful for forming papers, cloths, felts, mats, nonwoven fabrics, cordage, and the like.
Another important use for fibers formed by the ISF technique is as a coating and/or reinforcement for various substrates, such as loosely woven materials which require protection and strengthening. This procedure is commonly referred to as fiberizing or fiberization of the substrate. The fiberization of substrates is typically carried out by inefficient batch-type processes where the substrate is immersed in the polymer forming solution, agitated until the desired coating and/or impregnation of fibers has been achieved and then removed. In order to increase the commercial usefulness of ISF fiberization techniques, it would be desirable to provide a continuous production process in which the substrate to be fiberized is continually passed through the fiber forming solution in a manner which provides the desired fiber coating and/or impregnation.